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To: Sean Bruno <sbruno@miralink.com>
In-reply-to: Your message of "Fri, 29 Aug 2008 11:16:28 PDT."
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Date: Fri, 29 Aug 2008 13:21:25 +0100
From: Dieter <freebsd@sopwith.solgatos.com>
Cc: freebsd-firewire@freebsd.org
Subject: Re: This is where I'm going with fwcontrol 
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> > Should
> >
> >   
> >> Message ID  Root ID  R T Gap Count
> >>    00(2 bits)  (5 bits)    1 1    (6 bits)
> >>     
> >  
> > be
> >
> > Message ID   Root ID    R  T   Gap Count
> > 00(2 bits)   (6 bits)   1  1   (6 bits)
> >
> > send_phy_config() ANDs root_node with 0x3f, and the
> > "Physical ID" field in the controller register is
> > 6 bits.
> >   
> Well, according to the 1394 documentation, no.  The root ID is 
> definitely 5 bits.
> 
> The gap count is also 5 bits, I must have mis-counted.  So, really it 
> should be:
> 
> Message ID   Root ID    R  T   Gap Count
> 00(2 bits)   (5 bits)   1  1   (5 bits)

Looking at "Table 5. PHY Register Map" in the VIA controller datasheet
(page 24 of the pdf)
http://www.datasheetarchive.com/pdf-datasheets/Datasheets-6/DSA-113181.pdf

the "Physical ID" field is 6 bits, as is the "Gap Count" field.
I don't have the IEEE documentation, so I'll have to assume
you are correct about it saying 5 bits.  So why doesn't the
controller datasheet agree with the IEEE doc?  Granted one is
a controller register and the other is a packet, but I'd
expect these individual fields to be the same size.

> This means that the Root ID and the Gap Count cannot exceed 0x3f(63).

That's 6 bits.  5 bits would be 0x1f = 31 decimal.

> So, the masking
> of the values instead of generating and error seems wrong to me.  I'm 
> going to put in error checking
> to make sure the values comply with the specification and document the 
> correct values in the man page
> and the comments of the code.

Sounds good.